An automatic screw machine is a device in which a spindle is arranged to releasably hold a workpiece, and to rotate the workpiece relative to a tool. A Davenport® multi-spindle automatic screw machine has a rotating head with five such spindles arranged therein. (Davenport® is a registered trademark of Davenport Industries, Inc., now Davenport Machine, Inc., 167 Ames Street, Rochester, N.Y. 14611.) The head may be selectively rotated about its axis of elongation to angularly index the five spindles to various positions relative to various tools. When the head is in a particular angular position, each spindle therein is arranged in a particular station. As indicated above, the spindles are arranged to rotate relative to the head such that machining operations may be performed on the workpiece at the various stations.
These Davenport® multi-spindle automatic screw machines have existed in the prior art for many years. They are of a particularly durable and adaptable design, and have been improved and updated from time-to-time. Many of these devices are still in use today.
From time-to-time, it becomes necessary to replace the spindle assemblies on such Davenport® screw machines. Examples of prior art spindles are shown and described in U.S. Pat. No. 4,014,558, and in pending U.S. patent application Ser. No. 10/411,888, the aggregate disclosures of both of which are hereby incorporated by reference.
The present invention has largely evolved from a quest for greater accuracy. Indeed, with the inventive spindle disclosed herein, the target accuracy may be on the order of about 0.0003–0.0005 inches, as compared to a target accuracy of about 0.003 inches with prior art embodiments. Thus, the improved spindle affords an order of magnitude of improvement in precision and accuracy. Moreover, the improved spindle has a greater longevity. It wears better, is stiffer, allows greater rotational speeds, allows more aggressive machining cuts in the workpiece, and affords the capability of improved heat dissipation and lubrication.